WO2019177094A1 - ｃＢＮ焼結体および切削工具 - Google Patents

ｃＢＮ焼結体および切削工具 Download PDF

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WO2019177094A1
WO2019177094A1 PCT/JP2019/010528 JP2019010528W WO2019177094A1 WO 2019177094 A1 WO2019177094 A1 WO 2019177094A1 JP 2019010528 W JP2019010528 W JP 2019010528W WO 2019177094 A1 WO2019177094 A1 WO 2019177094A1
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cbn
sintered body
wsi
cbn sintered
volume
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PCT/JP2019/010528
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English (en)
French (fr)
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雅大 矢野
史朗 小口
庸介 宮下
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三菱マテリアル株式会社
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Priority to EP19767193.6A priority Critical patent/EP3766857A4/en
Priority to US16/979,477 priority patent/US11383305B2/en
Priority to CN201980016596.5A priority patent/CN111801304B/zh
Publication of WO2019177094A1 publication Critical patent/WO2019177094A1/ja

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    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23B—TURNING; BORING
    • B23B27/00—Tools for turning or boring machines; Tools of a similar kind in general; Accessories therefor
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Definitions

  • the present invention relates to a cubic boron nitride (hereinafter referred to as “cBN”)-based ultrahigh pressure sintered body (hereinafter referred to as “cBN sintered body”) having excellent toughness, and a cutting tool using the same as a tool base. (Hereinafter referred to as “CBN tool”).
  • CBN tool This application claims priority on March 14, 2018 based on Japanese Patent Application No. 2018-047247 for which it applied to Japan, and uses the content here.
  • cBN sintered bodies are known to be excellent in toughness and have low affinity with iron-based materials. Therefore, these tools are utilized to make cutting tools for steel-based work materials such as steel and cast iron. Widely used as a material.
  • Patent Document 1 describes a cBN sintered body having the following configuration.
  • A About 60 to 80% by volume of cBN having an average particle size of about 3 to 6 ⁇ m is included.
  • B about 40-20% by volume of ceramic binder phase, and (i) about 20-60% by volume of said ceramic binder phase of a Group 4B or Group 6B metal carbide, nitride, or boride.
  • Ii about 40-80% by volume of the ceramic binder phase is one or more of aluminum carbide, nitride, boride or oxide.
  • C contains about 3 to 15% by weight of tungsten, and the XRD intensity ratio of the [101] TiB 2 peak and the [110] WB peak is less than about 0.4.
  • the cBN sintered body described in Patent Document 2 has 20% by volume or more and 80% by volume or less cubic boron nitride particles and a binder, and the binder includes a group 4a element in the periodic table, At least one selected from the group consisting of nitrides, carbides, borides, oxides, and solid solutions of Group 5a elements, Group 6a elements, and Zr, Si, Hf, Ge, W, and Co.
  • the W and And / or the total weight of Co is less than 2.0% by weight and contains any one or more of Zr, Si, Hf, and Ge (hereinafter referred to as “X”), Each 0.005 wt% or more and less than 2.0 wt%, and / (X + W + Co) satisfies 0.01 or more and 1.0 or less, and at most 20.0 wt% by weight 2.0% by weight or more of Al.
  • JP 2004-160637 A Japanese Patent No. 5189504
  • the cBN sintered body described in Patent Document 1 contains W in the sintered body, a Ti boride (TiB 2 ) phase and a W boride (WB) phase are simultaneously generated during sintering.
  • the produced W boride phase suppresses the formation of Ti boride phase at the cBN particle-binding phase interface, and the XRD intensity ratio between the [101] TiB 2 peak and the [110] WB peak is suppressed to less than about 0.4. .
  • the adhesiveness at the interface of the cBN particles and the binder phase is reduced, and this serves as a starting point for occurrence of cracks, thereby reducing toughness and fracture resistance.
  • the cBN sintered body described in Patent Document 2 contains a predetermined amount of W and / or Co, Si, or Zr in the binder phase in order to increase the strength and toughness of the binder phase. If the proportion of the content in the sintered body is large, the toughness in the sintered body decreases. If the amount of Si is large, the diffusion reaction of the binder is excessively suppressed, and the bonding strength between the cBN particles, the binder, and the binder is reduced. There was a problem that the toughness of the body was lowered. In addition, when the dispersibility during mixing is poor, a part with a high concentration of the additive is locally generated, and the toughness of the bonding material at that part is lowered. There was a problem that decreased.
  • An object of the present invention is to solve the problem that the cBN sintered body cannot secure sufficient toughness in the above prior art, and to provide a cBN sintered body having high toughness and a CBN tool using this as a tool base.
  • a cBN sintered body and a CBN tool using the same as a tool base have a cBN particle-bonded phase interface even if the cBN sintered body contains a W compound.
  • Intensive study was conducted on dispersed particles that do not cause a decrease in adhesion. As a result, it was found that if particles that do not become a reaction product with cBN grains are dispersed, the formation of a Ti boride phase generated at the interface between the cBN particles and the binder phase is not inhibited.
  • WSi 2 particles are suitable, and fine WSi 2 particles having a specific average particle size range are dispersed in the binder phase of the cBN sintered body, thereby causing cracks in the sintered body. Even when it has occurred, it has been newly found that the progress of cracks can be finely bypassed by WSi 2 , the linear progress can be suppressed, and a cBN sintered body having high toughness can be obtained. It has also been found that when this cBN sintered body is used as a tool base of a cutting tool, the cutting edge is not easily damaged even when intermittent cutting with a large load on the cutting edge is performed.
  • a first aspect of the present invention is a cBN sintered body, the cBN sintered body comprising cubic boron nitride particles and a ceramic binder phase, and the cBN sintered body has an average grain size.
  • WSi 2 having a diameter of 10 nm or more and 200 nm or less is dispersed so that the content ratio is 1 volume% or more and 20 volume% or less.
  • Another aspect of the present invention is a cutting tool, and the cutting tool uses the cBN sintered body described in (1) as a tool base.
  • a reaction product with cBN particles that is, WSi 2 fine particles not containing B and N as components, is dispersed, so that a Ti boride phase generated at the cBN particle-binding phase interface.
  • the progress of cracks generated in the sintered body is finely bypassed by WSi 2 dispersed in the sintered body. , Exerts the effect of suppressing the linear progress of cracks and increasing toughness.
  • the cutting tool according to the present invention uses the cBN sintered body as a tool base, so that the cutting edge is not easily damaged even when intermittent cutting with a large load on the cutting edge is performed.
  • intermittent cutting of high-hardness steel Also in processing, it has excellent wear resistance and excellent fracture resistance over a long period of use.
  • cBN sintered body is a schematic diagram showing the distribution of WSi 2 contained in the sintered structure, the shape of each tissue, the dimensions are not conforming to the actual tissue. It is a figure which shows an example of XRD (X-ray Diffraction) of this invention sintered compact 9 as cBN sintered compact concerning this invention.
  • XRD X-ray Diffraction
  • the average particle size of the cBN particles used in the present invention is not particularly limited, but is preferably in the range of 0.2 to 8.0 ⁇ m.
  • the average particle size of the cBN particles used in the present invention is not particularly limited, but is preferably in the range of 0.2 to 8.0 ⁇ m.
  • the average particle size of the cBN particles can be determined as follows.
  • the cross-sectional structure of the cBN sintered body is observed with a scanning electron microscope (SEM) to obtain a secondary electron image.
  • SEM scanning electron microscope
  • the portion of the cBN particles in the obtained image is extracted by image processing, and the average particle size is calculated based on the maximum length of each particle determined by image analysis.
  • Binarization processing is performed so that the cBN grain is black using an image of a pixel that is displayed in monochrome and has a ratio between the pixel value of the cBN particle portion and the pixel value of the binder phase portion of 2 or more.
  • an average value obtained from an average value in an area of about 0.5 ⁇ m ⁇ 0.5 ⁇ m is obtained, and an average value obtained from at least three different points in the same image is obtained. It is desirable to use it for each contrast.
  • a process that separates the parts considered to be in contact with the cBN grains for example, by spreading the center of a region called a watershed (watershed algorithm / mark) to adjacent pixels.
  • the cBN grains that appear to be in contact are separated using an algorithm for obtaining a region.
  • the part corresponding to the cBN grains (black part) in the image obtained after the binarization processing is subjected to particle analysis, and the obtained maximum length is set as the maximum length of each particle, which is the diameter of each particle.
  • particle analysis for obtaining the maximum length for example, a value of a large length from two lengths obtained by calculating the ferret diameter for one cBN particle is set as the maximum length, and the value is set as the diameter of each particle. To do. Assuming an ideal sphere having this diameter, the volume obtained by calculation is determined as the volume of each particle, and the cumulative volume is obtained. Based on this cumulative volume, the vertical axis is volume percentage [%] and the horizontal axis is diameter [ ⁇ m] Draw.
  • the diameter when the volume percentage was 50% was defined as the average particle size of cBN particles, and this was performed for three observation regions, and the average value was defined as the average particle size [ ⁇ m] of cBN.
  • a length ( ⁇ m) per pixel is set using a scale value known in advance by SEM.
  • the observation area used for image processing is preferably a visual field area of about 15.0 ⁇ m ⁇ 15.0 ⁇ m when the average particle size of cBN particles is 3 ⁇ m.
  • the content ratio of the cBN particles in the cBN sintered body is not particularly limited, but if it is less than 40% by volume (vol%), the sintered body has a small amount of hard material, and when used as a tool, On the other hand, when the volume exceeds 78% by volume, voids serving as starting points of cracks are generated in the sintered body, and the chip resistance may be lowered. Therefore, in order to further exhibit the effects exhibited by the present invention, the content ratio of cBN particles in the cBN sintered body is preferably in the range of 40 to 78% by volume.
  • WSi 2 dispersed in cBN sintered body The WSi 2 dispersed in the cBN sintered body will be described.
  • (1) average particle sizes of WSi 2 is a 10nm or 200nm or less. The reason for this range is that if the average particle size exceeds 200 nm, cracks starting from WSi 2 particles in the binder phase are likely to be generated and propagated. This is because if the diameter is less than 10 nm, it is not possible to sufficiently circumvent the crack and suppress its progress.
  • the average particle diameter of WSi 2 is more preferably 10 nm or more and 160 nm or less.
  • Content ratio WSi 2 is present in the cBN sintered body at a content ratio of 1% by volume to 20% by volume.
  • the reason for this range being less than 1% by volume is that the crack is finely bypassed and the progress thereof cannot be sufficiently suppressed, and the amount is not sufficient to improve the toughness of the cBN sintered body, but 20 volume.
  • % probability of WSi 2 are in contact with each other in more than the sintered body in increases, next WSi 2 hypertrophy and WSi 2 next to each other are bonded during sintering, the occurrence of cracks starting from the its enlargement of WSi 2 This is because it tends to occur and the toughness of the cBN sintered body decreases.
  • the content ratio is more preferably 3% by volume or more and 15% by volume or less.
  • a procedure for producing a cBN sintered body having excellent toughness according to the present invention is shown below.
  • a raw material powder constituting the binder phase a WSi 2 raw material and a main raw material of the binder phase are prepared.
  • a WSi 2 powder having an average particle diameter of 3 ⁇ m is prepared as a WSi 2 raw material.
  • a container lined with cemented carbide is filled with cemented carbide balls and acetone, capped, and then pulverized by a ball mill.
  • conventionally known binder phase forming raw material powders TiN powder, TiC powder, TiCN powder, TiAl 3 powder, Al 2 O 3 powder are prepared as raw materials for the binder phase.
  • the obtained sintered body raw material powder is molded at a predetermined pressure to produce a molded body, which is temporarily sintered at 1000 ° C., and then mounted in an ultrahigh pressure sintering apparatus.
  • the cBN sintered body of the present invention is manufactured by sintering at a predetermined temperature within a range of pressure: 5 GPa and temperature: 1200 to 1600 ° C.
  • the cutting tool made of a cBN-based ultra-high-pressure sintered body using a cBN sintered body having excellent toughness as a tool base according to the present invention has excellent fracture resistance and is used for a long time even in intermittent cutting of high-hardness steel, for example. Excellent wear resistance over time.
  • AES Auger Electron Spectroscopy
  • the calculation of the average particle diameter of WSi 2 is as follows. In one image, the ferret diameter of each particle in which a portion where the W element and the Si element overlap is recognized as WSi 2 based on the mapping image of the W element and the Si element, To do. Based on the volume of each particle calculated and obtained from this diameter, the cumulative volume is obtained in the same manner as cBN, and the graph is drawn with the vertical axis as volume percentage [%] and the horizontal axis as diameter [ ⁇ m] from this cumulative volume. The diameter when the percentage is 50% is defined as the average particle diameter of WSi 2 in one image used for measurement. This was performed on three images, and the average value was taken as the average particle size [ ⁇ m] of WSi 2 . When performing particle analysis, a length ( ⁇ m) per pixel is set using a scale value known in advance by AES. As an observation area used for image processing, a visual field area of about 5.0 ⁇ m ⁇ 3.0 ⁇ m is desirable.
  • the content ratio of WSi 2 in the cBN sintered body is obtained by calculating the cross-sectional structure of the cBN sintered body from the mapping image of W element and Si element by AES. In the observed one image, the portion W element and Si element overlaps extracted by image processing as WSi 2, and calculates the area occupied by the WSi 2 by image analysis to determine the ratio of WSi 2 occupied. This is performed on at least three images, and the average value of the calculated area ratio of each WSi 2 is obtained as the WSi 2 content ratio in the cBN sintered body. As an observation area used for image processing, a visual field area of about 5.0 ⁇ m ⁇ 3.0 ⁇ m is desirable.
  • WSi 2 powder is prepared as a raw material powder for constituting the binder phase, and subjected to pulverization with a ball mill for controlling the particle size of WSi 2 .
  • WSi 2 raw material powder having a desired particle size range was prepared by classification using a centrifugal separation method. That is, WSi 2 powder having an average particle size of 3 ⁇ m was prepared, filled with a cemented carbide ball and acetone in a cemented carbide container, capped, ground using a ball mill, and mixed. After drying the slurry, it is classified using a centrifugal separator to obtain a WSi 2 raw material powder having an average particle diameter of 50 to 200 nm.
  • the obtained sintered body raw material powder was press-molded at a molding pressure of 1 MPa to a size of diameter: 50 mm ⁇ thickness: 1.5 mm, and then this molded body was 1000 ° C. in a vacuum atmosphere at a pressure of 1 Pa or less.
  • the materials shown in Table 2 are preliminarily sintered while being held at a predetermined temperature within the range of, and then charged into an ultra-high pressure sintering apparatus and sintered at a pressure of 5 GPa and a temperature of 1400 ° C.
  • inventive sintered bodies 1 to 12 (referred to as inventive sintered bodies 1 to 12) were produced.
  • the main purpose of the heat treatment applied to the compact is to remove the solvent during wet mixing.
  • a molded body is produced under the same conditions as the sintered bodies 1 to 12 of the present invention, heat-treated, and these molded bodies are sintered at ultrahigh pressure and high temperature under the same conditions as the sintered bodies 1 to 12 of the present invention.
  • cBN sintered bodies of comparative examples hereinafter referred to as comparative example sintered bodies 1 to 5 shown in Table 4 were produced.
  • the inventive sintered bodies 1 to 12 and the comparative example sintered bodies 1 to 5 produced above were cut into predetermined dimensions with a wire electric discharge machine.
  • TaC 5% by mass
  • WC WC-based cemented carbide insert body having the remaining composition and ISO standard CNGA120408 insert shape is manufactured, and brazed portions (corner portions) of each insert body
  • the sintered bodies 1 to 12 of the present invention and the sintered bodies 1 to 5 of the comparative example are brazed using a brazing material of an Ag alloy having a composition of Cu: 26 mass%, Ti: 5 mass%, and Ag: the remainder.
  • the upper and lower surfaces and the outer periphery are polished, and the honing process is performed.
  • CBN-based ultra-high pressure sintered body cutting tools (referred to as comparative tools) 1 to 5 were produced.
  • the tool of the present invention had a longer tool life and improved toughness without the occurrence of sudden chipping of the cutting edge compared to the comparative tool. Even in intermittent cutting of high-hardness steel, the tool of the present invention has an excellent effect of being excellent in wear resistance and having excellent fracture resistance over a long period of use. .
  • the cBN sintered body of the present invention When used as a tool base of a CBN tool, it exhibits excellent fracture resistance over a long period of use without causing any chipping of the tool base, thereby extending the tool life. Therefore, it is possible to improve the performance of the cutting device and to save the labor and energy of the cutting process and to reduce the cost, so that it can be used industrially.

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Abstract

このｃＢＮ焼結体は、立方晶窒化ほう素粒子およびセラミックス結合相からなるｃＢＮ焼結体であって、平均粒径が１０ｎｍ以上２００ｎｍ以下のＷＳｉ２が、前記焼結体に、その含有割合が１体積％以上２０体積％以下となるように分散されている。切削工具は、前記ｃＢＮ焼結体を工具基体として有する。

Description

ｃＢＮ焼結体および切削工具
　本発明は、靭性に優れた立方晶窒化ほう素（以下、「ｃＢＮ」で示す）基超高圧焼結体（以下、「ｃＢＮ焼結体」という）、および、これを工具基体とする切削工具（以下、「ＣＢＮ工具」という）に関する。
　本願は、２０１８年３月１４日に、日本に出願された特願２０１８－０４７２４７号に基づき優先権を主張し、その内容をここに援用する。
　従来から、ｃＢＮ焼結体は、靭性に優れることが知られており、鉄系材料との親和性が低いことから、これらの特性を活かし、鋼、鋳鉄等の鉄系被削材の切削工具材料として広く用いられている。
　例えば特許文献１には、下記の構成を有するｃＢＮ焼結体が記載されている。
（ａ）平均粒度約３～６μｍのｃＢＮを約６０～８０体積％含む。
（ｂ）セラミック結合剤相を約４０～２０体積％含み、（ｉ）前記セラミック結合剤相の約２０～６０体積％が第４Ｂ族又は第６Ｂ族金属の炭化物、窒化物、又はホウ化物の１種以上であり、（ｉｉ）前記セラミック結合剤相の約４０～８０体積％がアルミニウムの炭化物、窒化物、ホウ化物又は酸化物の１種以上である。
（ｃ）タングステンを約３～１５重量％を含み、［１０１］ＴｉＢ２ピークと［１１０］ＷＢピークのＸＲＤ強度比が約０．４未満である。
　また、特許文献２に記載されたｃＢＮ焼結体は、２０体積％以上８０体積％以下の立方晶窒化硼素粒子と結合材とを有し、前記結合材は、周期律表第４ａ族元素、第５ａ族元素、第６ａ族元素の窒化物、炭化物、硼化物、酸化物、およびこれらの固溶体からなる群の中から選択された少なくとも一種と、Ｚｒ、Ｓｉ、Ｈｆ、Ｇｅ、Ｗ、Ｃｏの単体、化合物、および固溶体からなる群の中から選択された少なくとも１種と、Ａｌの化合物とからなり、前記複合焼結体中にＷ及び／又はＣｏが含有される場合には、該Ｗ及び／又はＣｏの合計重量は２．０重量％未満であり、かつ前記Ｚｒ、Ｓｉ、Ｈｆ、Ｇｅ（以下、「Ｘ」とする。）のいずれか一以上を含有し、前記Ｘは各元素がそれぞれ０．００５重量％以上２．０重量％未満であり、かつＸ／（Ｘ＋Ｗ＋Ｃｏ）が０．０１以上１．０以下を満たし、かつＡｌの重量が２．０重量％以上２０．０重量％以下である。
特開２００４－１６０６３７号公報 特許第５１８９５０４号公報
　特許文献１に記載されたｃＢＮ焼結体は、焼結体中にＷを含有するため、焼結に際し、Ｔｉ硼化物（ＴｉＢ２）相とＷ硼化物（ＷＢ）相を同時に生成する。生成したＷ硼化物相は、ｃＢＮ粒子－結合相界面のＴｉ硼化物相の生成を抑制し、［１０１］ＴｉＢ２ピークと［１１０］ＷＢピークのＸＲＤ強度比が約０．４未満に抑えられる。このため、ｃＢＮ粒子－結合相界面の付着力が低下し、これがクラック発生の起点となることによって、靱性や耐欠損性が低下するという問題があった。
　特許文献２に記載されたｃＢＮ焼結体は、結合相の強度と靱性を高めるためにＷ及び／又はＣｏ、Ｓｉ又はＺｒを結合相中に所定量含有させているが、Ｗが焼結体中に占める割合が多いと焼結体中の靱性が低下し、Ｓｉが多いと結合材の拡散反応が過剰に抑制され、ｃＢＮ粒子と結合材、および結合材同士の結合力が低下し、焼結体の靱性が低下する問題があった。また、混合時の分散性が悪いと局所的に添加物の濃度が高い部分が生じ、その部分の結合材の靱性が低下し、工具として使用した場合、破壊の起点となることによって耐欠損性が低下するという問題があった。
　本発明は、上記先行技術においてｃＢＮ焼結体が十分な靱性を確保できないという課題を解決し、靱性の高いｃＢＮ焼結体およびこれを工具基体とするＣＢＮ工具を提供することを目的とする。
本発明者は、ｃＢＮ焼結体およびこれを工具基体とするＣＢＮ工具について、上記課題を解決するために、ｃＢＮ焼結体中にＷ化合物を含有していても、ｃＢＮ粒子－結合相界面の付着力の低下を生じさせない分散粒子について鋭意検討を行った。その結果、ｃＢＮ粒との反応生成物とはならない粒子を分散させれば、ｃＢＮ粒子－結合相界面に生じるＴｉ硼化物相の生成を阻害しないことを見いだした。また、この粒子として、ＷＳｉ２粒子が適切であること、特定の平均粒径範囲にある微細なＷＳｉ２粒子をｃＢＮ焼結体の結合相中に分散させることによって、焼結体内にてクラックが生じた場合にも、クラックの進展はＷＳｉ２により細かく迂回し、直線的な進展を抑えることができ、靱性の高いｃＢＮ焼結体を得ることができることを新たに見出した。また、このｃＢＮ焼結体を切削工具の工具基体として用いた場合、刃先への負荷の大きい断続切削を行っても刃先が欠損しにくいということも見出した。
本発明は、上記各知見に基づいてなされたものであって、下記の構成を特徴としている。
（１）本発明の第１の態様はｃＢＮ焼結体であって、このｃＢＮ焼結体は、立方晶窒化ほう素粒子とセラミックス結合相からなり、前記ｃＢＮ焼結体中には、平均粒径が１０ｎｍ以上２００ｎｍ以下のＷＳｉ２が、含有割合が１体積％以上２０体積％以下となるように分散している。
（２）本発明の他の態様は切削工具であって、この切削工具は、前記（１）に記載のｃＢＮ焼結体を工具基体とする。
　本発明に係るｃＢＮ焼結体では、ｃＢＮ粒子との反応生成物、すなわちＢとＮをその構成成分に含まないＷＳｉ２の微粒子を分散させるため、ｃＢＮ粒子－結合相界面に生じるＴｉ硼化物相の生成が阻害されず、ｃＢＮ粒子－結合相界面の付着力を低下させないことに加えて、焼結体内で生じたクラックの進展を焼結体中に分散させたＷＳｉ２により細かく迂回させることで、クラックの直線的な進展を抑えて靱性を高めるという効果を発揮する。
　また、本発明に係る切削工具は、前記ｃＢＮ焼結体を工具基体として用いたことにより、刃先への負荷の大きい断続切削を行っても刃先が欠損しにくく、例えば、高硬度鋼の断続切削加工においても、耐摩耗性に優れ、長期の使用にわたって優れた耐欠損性を有する。
本発明に係るｃＢＮ焼結体の一実施形態において、焼結組織に含まれるＷＳｉ２の分散を示す模式図であり、各組織の形状、寸法は実際の組織に則したものではない。 本発明に係るｃＢＮ焼結体として、本発明焼結体９のＸＲＤ（X-ray Diffraction）の一例を示す図である。
　以下、本発明を詳細に説明する。なお、本明細書において、数値範囲を「～」を用いて表現する場合、その範囲は上限および下限の数値を含む。
［ｃＢＮ粒子の平均粒径］
　本発明で用いるｃＢＮ粒子の平均粒径は、特に限定されるものではないが、０．２～８．０μｍの範囲であることが好ましい。これにより、硬質なｃＢＮ粒子を焼結体内に含むから、耐欠損性を高める効果が得られる。また、平均粒径が０．２～８．０μｍのｃＢＮ粒子を焼結体内に分散させることにより、工具使用中に工具表面のｃＢＮ粒子が脱落して生じる刃先の凹凸形状を起点とする欠損、チッピングを抑制する。さらに、工具使用中に刃先に加わる応力により生じるｃＢＮ粒子と結合相との界面から進展するクラック、あるいはｃＢＮ粒子が割れて進展するクラックの伝播を抑制することにより、優れた耐欠損性を有することができる。
　ｃＢＮ粒子の平均粒径は、以下のとおりにして求めることができる。
　ｃＢＮ焼結体の断面組織を走査型電子顕微鏡（ＳＥＭ）にて観察し、二次電子像を得る。得られた画像内のｃＢＮ粒子の部分を画像処理にて抜き出し、画像解析より求めた各粒子の最大長を基に平均粒径を算出する。画像内のｃＢＮ粒子の部分を画像処理にて抜き出すにあたり、ｃＢＮ粒子と結合相とを明確に判断するため、画像中の黒い画素の値を０、白い画素の値を２５５として、２５６階調のモノクロで表示し、ｃＢＮ粒子部分の画素の値と、結合相部分の画素の値の比が２以上となる値の画素の像を用いて、ｃＢＮ粒が黒となるように２値化処理を行う。
　ｃＢＮ粒子部分や結合相部分の画素値を求めるための領域として、０．５μｍ×０．５μｍ程度の領域内の平均値より求め、少なくとも同一画像内から、異なる３個所より求めた平均の値を各々のコントラストとして使用することが望ましい。
　なお、２値化処理後はｃＢＮ粒同士が接触していると考えられる部分を切り離すような処理、例えば、ウォーターシェッド（watershedアルゴリズム／マークと呼ばれる領域の中心を隣接画素へと広げていくことによって領域を得るアルゴリズム）を用いて接触していると思われるｃＢＮ粒同士を分離する。
　２値化処理後に得られた画像内のｃＢＮ粒にあたる部分（黒の部分）を粒子解析し、求めた最大長を各粒子の最大長とし、それを各粒子の直径とする。最大長を求める粒子解析としては、例えば、１つのｃＢＮ粒子に対してフェレ径を算出することより得られる２つの長さから大きい長さの値を最大長とし、その値を各粒子の直径とする。この直径を有する理想球体と仮定して計算より求めた体積を各粒子の体積として累積体積を求め、この累積体積を基に縦軸を体積百分率［％］、横軸を直径［μｍ］としてグラフを描画する。このグラフ上で体積百分率が５０％のときの直径をｃＢＮ粒子の平均粒径とし、これを３つの観察領域に対して行い、その平均値をｃＢＮの平均粒径［μｍ］とした。粒子解析を行う際には、あらかじめＳＥＭにより分かっているスケールの値を用いて、１ピクセル当たりの長さ（μｍ）を設定しておく。画像処理に用いる観察領域は、ｃＢＮ粒子の平均粒径が３μｍの場合、１５.０μｍ×１５.０μｍ程度の視野領域が望ましい。
［ｃＢＮ焼結体に占めるｃＢＮ粒子の含有割合］
　ｃＢＮ焼結体に占めるｃＢＮ粒子の含有割合は、特に限定されるものではないが、４０体積％（ｖｏｌ％）未満では、焼結体中に硬質物質が少なく、工具として使用した場合に、耐欠損性が低下することがあり、一方、７８体積％を超えると、焼結体中にクラックの起点となる空隙が生成し、耐欠損性が低下することがある。そのため、本発明が奏する効果をより一層発揮するためには、ｃＢＮ焼結体に占めるｃＢＮ粒子の含有割合は、４０～７８体積％の範囲とすることが好ましい。
［ｃＢＮ焼結体中に分散させるＷＳｉ２］
　ｃＢＮ焼結体中に分散させるＷＳｉ２について説明する。
（１）平均粒径
　ＷＳｉ２の平均粒径は、１０ｎｍ以上２００ｎｍ以下とする。この範囲とした理由は、平均粒径が２００ｎｍを超えると、結合相中のＷＳｉ２粒子を起点とするクラックの発生や進展が生じやすくなるため、ｃＢＮ焼結体の靱性が低下し、平均粒径１０ｎｍ未満であると、クラックを細かく迂回させてその進展を抑制することが十分にできないためである。ＷＳｉ２の平均粒径は、１０ｎｍ以上１６０ｎｍ以下がより望ましい。
（２）含有割合
　ＷＳｉ２は、ｃＢＮ焼結体中に１体積％以上２０体積％以下の含有割合で存在する。この範囲とした理由は、１体積％未満であるとクラックを細かく迂回させてその進展を抑制することが十分にできずｃＢＮ焼結体の靱性を向上させるには十分な量ではなく、２０体積％を超えると焼結体中においてＷＳｉ２同士が接する確率が多くなり、隣り合ったＷＳｉ２が焼結時に結合して肥大なＷＳｉ２となり、その肥大なＷＳｉ２を起点としたクラックの発生が生じやすくなり、ｃＢＮ焼結体の靱性が低下してしまうためである。含有割合は、３体積％以上１５体積％以下がより望ましい。
［ｃＢＮ焼結体の製造方法］
　本発明の靭性に優れたｃＢＮ焼結体を作製するための手順の一例を次に示す。
（１）結合相を構成する成分の原料粉末の準備
　結合相を構成する原料粉末として、ＷＳｉ２原料と結合相の主となる原料を用意する。ＷＳｉ２原料として、平均粒径３μｍのＷＳｉ２粉末を用意する。ＷＳｉ２粉末は、所望の粒径に粉砕したＷＳｉ２原料粉とするため、例えば、超硬合金で内張りされた容器内に超硬合金製ボールとアセトンと共に充填し、蓋をした後にボールミルにより粉砕を行った後、遠心分離装置を用いて分級することにより、縦軸を体積百分率、横軸を粒子径とした場合のメディアン径Ｄ５０を粉砕したＷＳｉ２原料粉の平均粒径とし、その値が１０～２００ｎｍのＷＳｉ２原料粉を得る。また、結合相の主となる原料としては、従来から知られている結合相形成原料粉末（ＴｉＮ粉末、ＴｉＣ粉末、ＴｉＣＮ粉末、ＴｉＡｌ３粉末、Ａｌ２Ｏ３粉末）を準備する。
（２）粉砕・混合
　これらの原料粉末を、例えば、超硬合金で内張りされた容器内に超硬合金製ボールとアセトンと共に充填し、蓋をした後にボールミルにより粉砕および混合を行う。その後、硬質相として機能させる平均粒径０．２～８．０μｍのｃＢＮ粉末を添加して、さらに、ボールミル混合を行う。
（３）成形、焼結
　次いで、得られた焼結体原料粉末を、所定圧力で成形して成形体を作製し、これを１０００℃で仮焼結し、その後、超高圧焼結装置に装入して、例えば、圧力：５ＧＰａ、温度：１２００～１６００℃の範囲内の所定の温度で焼結することにより、本発明のｃＢＮ焼結体を作製する。
［ＣＢＮ工具］
　本発明の、靭性に優れたｃＢＮ焼結体を工具基体とするｃＢＮ基超高圧焼結体製切削工具は、例えば、高硬度鋼の断続切削加工においても、耐欠損性に優れ、長期の使用にわたって優れた耐摩耗性を発揮する。
［各数値の測定方法］
　本発明で特定している各数値の測定方法について説明する。
［ＷＳｉ２の平均粒径］
　ＷＳｉ２の平均粒径測定のため、ｃＢＮ焼結体の断面組織をオージェ電子分光法（Auger Electron Spectroscopy：以下、ＡＥＳという）を用いて、Ｗ元素とＳｉ元素のマッピング像を得る。得られた画像において、Ｗ元素とＳｉ元素が重なる部分を画像処理にて抜き出し、画像解析より特定した各粒子を基に平均粒径を算出する。
　ＷＳｉ２の平均粒径の算出は１画像において、Ｗ元素とＳｉ元素のマッピング像を基にＷ元素とＳｉ元素が重なる部分をＷＳｉ２と認識した各粒子のフェレ径を、各粒子の直径とする。この直径より計算し求めた各粒子の体積を基に累積体積をｃＢＮと同様に求め、この累積体積より縦軸を体積百分率［％］、横軸を直径［μｍ］としてグラフを描画させ、体積百分率が５０％のときの直径を測定に用いた１画像内のＷＳｉ２の平均粒径とする。これを３つの画像に対して行い、その平均値をＷＳｉ２の平均粒径［μｍ］とした。粒子解析を行う際には、あらかじめＡＥＳにより分かっているスケールの値を用いて、１ピクセル当たりの長さ（μｍ）を設定しておく。画像処理に用いる観察領域としては、５.０μｍ×３.０μｍ程度の視野領域が望ましい。
［焼結体中のＷＳｉ２の含有割合］
　ｃＢＮ焼結体に占めるＷＳｉ２の含有割合は、ｃＢＮ焼結体の断面組織をＡＥＳによってＷ元素とＳｉ元素のマッピング像より算出し求める。観察した１画像において、Ｗ元素とＳｉ元素が重なる部分をＷＳｉ２として画像処理にて抜き出し、画像解析によってＷＳｉ２が占める面積を算出し、ＷＳｉ２が占める割合を求める。これを少なくとも３つの画像に対して行い、算出した各ＷＳｉ２の面積割合の平均値をｃＢＮ焼結体に占めるＷＳｉ２の含有割合として求める。画像処理に用いる観察領域として、５．０μｍ×３．０μｍ程度の視野領域が望ましい。
　以下に、本発明の実施例について記載する。
　本実施形態のｃＢＮ焼結体の製造では、結合相を構成するための原料粉末として、ＷＳｉ２粉末を準備し、ＷＳｉ２の粒径制御のため、ボールミルにて粉砕の処理を施した後、遠心分離法を用いて分級することにより所望の粒径範囲のＷＳｉ２原料粉を用意した。すなわち、平均粒径３μｍのＷＳｉ２粉末を準備し、超硬合金で内張りされた容器内に超硬合金製ボールとアセトンと共に充填し、蓋をした後にボールミルを用いて粉砕を実施後、混合したスラリーを乾燥させた後、遠心分離装置を用いて分級することにより平均粒径が５０～２００ｎｍのＷＳｉ２原料粉を得ることができる。
　上記のように事前に準備したＷＳｉ２原料粉と、平均粒径が０．３μｍ～０．９μｍのＴｉＮ粉末、ＴｉＣ粉末、ＴｉＣＮ粉末、ＴｉＡｌ３粉末、Ａｌ２Ｏ３粉末を用意し、これら原料粉末の中から選ばれたいくつかの結合相構成用原料粉末（各原料粉末の体積％を表１に示す）と、硬質相用原料としてのｃＢＮ粉末の合量を１００体積％としたときの焼結後のｃＢＮ粒子の含有割合が４０～７８体積％となるように配合し、湿式混合し、乾燥した。
　次いで、得られた焼結体原料粉末を、成形圧１ＭＰａで直径：５０ｍｍ×厚さ：１．５ｍｍの寸法にプレス成形し、ついでこの成形体を、圧力：１Ｐａ以下の真空雰囲気中、１０００℃の範囲内の所定温度に保持して仮焼結し、その後、超高圧焼結装置に装入して、圧力：５ＧＰａ、温度：１４００℃の温度で焼結することにより、表２に示す本発明のｃＢＮ焼結体１～１２（本発明焼結体１～１２という）を作製した。成形体に施す熱処理は、湿式混合時の溶媒を除去することが主な目的である。また、上記作製工程は、本実施例のように超高圧焼結までの工程において原料粉末の酸化を防止することが好ましく、具体的には非酸化性の保護雰囲気中での取り扱いを実施することが好ましい。本発明焼結体９のＸＲＤ図を図２に示す。
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
　比較のため、（１）ＷＳｉ２を含まない場合、（２）ＷＳｉ２原料をボールミルを用いて粉砕し、遠心分離装置を用いて分級し得た、本発明において規定する範囲外の平均粒径のＷＳｉ２原料粉を用いた場合、（３）本発明において規定する範囲内の平均粒径のＷＳｉ２原料粉を用い、本発明において規定する範囲外のＷＳｉ２含有割合を有する場合をそれぞれ検討した。これらＷＳｉ２（含まない場合がある）と、平均粒径０．３μｍ～０．９μｍのＴｉＮ粉末、ＴｉＣ粉末、ＴｉＣＮ粉末、ＴｉＡｌ３粉末、およびＡｌ２Ｏ３粉末を用意した。これら原料粉末の中から選ばれたいくつかの結合相構成用原料粉末（各原料粉末の体積％を表３に示す）と、硬質相としてのｃＢＮ粉末とを湿式混合し、得られた混合物を乾燥させた。両者の配合率は、前記混合物の含量を１００体積％としたときの焼結後のｃＢＮ粒子の含有割合が５８～６３体積％となるようにした。
　その後、本発明焼結体１～１２と同様な条件で成形体を作製し、熱処理し、これらの成形体を、本発明焼結体１～１２と同様な条件で超高圧高温焼結することにより、表４に示す比較例のｃＢＮ焼結体（以下、比較例焼結体という）１～５を作製した。
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
　次に、上記で作製した本発明焼結体１～１２、比較例焼結体１～５を、ワイヤー放電加工機で所定寸法に切断した。Ｃｏ：５質量％、ＴａＣ：５質量％、ＷＣ：残りの組成およびＩＳＯ規格ＣＮＧＡ１２０４０８のインサート形状をもったＷＣ基超硬合金製インサート本体を製造し、各インサート本体のろう付け部（コーナー部）に、本発明焼結体１～１２、比較例焼結体１～５を、Ｃｕ：２６質量％、Ｔｉ：５質量％、Ａｇ：残りからなる組成を有するＡｇ合金のろう材を用いてろう付けし、上下面および外周研磨、ホーニング処理を施すことにより、ＩＳＯ規格ＣＮＧＡ１２０４０８のインサート形状をもつ本発明のｃＢＮ基超高圧焼結体切削工具（本発明工具という）１～１２、および、比較例のｃＢＮ基超高圧焼結体切削工具（比較工具という）１～５を製造した。
　次いで、本発明工具１～１２と比較工具１～５に対して、以下の切削条件で切削加工を実施し、欠損に至るまでの工具寿命（断続回数）を測定した。
　＜切削条件＞
被削材：浸炭焼き入れ鋼（ＪＩＳ・ＳＣＭ４１５、硬さ：ＨＲＣ５８～６２）の長さ方向等間隔８本縦溝入り丸棒、
切削速度：２００ｍ／ｍｉｎ、
切り込み：０．１ｍｍ、
送り：０．１ｍｍ／ｒｅｖ
　上記条件での、高硬度鋼の乾式切削加工試験を実施。各工具の刃先がチッピングあるいは欠損に至るまでの断続回数を工具寿命とし、断続回数５００回毎に刃先を観察し、刃先の欠損やチッピングの有無を確認した。表５に、上記切削加工試験の結果を示す。
Figure JPOXMLDOC01-appb-T000005
　表５に示される結果から、本発明工具は、比較工具に比して、突発的な刃先のチッピングが発生することなく、工具寿命が延命化されており、靱性が向上したことが分かった。高硬度鋼の断続切削加工においても、本発明工具は、耐摩耗性に優れ、長期の使用にわたって優れた耐欠損性を有するという優れた効果を奏した。。
　本発明のｃＢＮ焼結体は、ＣＢＮ工具の工具基体として用いた場合に、工具基体の欠損を発生することなく長期の使用にわたって、優れた耐欠損性を発揮し、工具寿命の延命化が図られるものであり、切削加工装置の高性能化、並びに切削加工の省力化および省エネ化、低コスト化が図れるから、産業上の利用が可能である。
 

Claims (2)

  1. 　立方晶窒化ほう素粒子とセラミックス結合相からなるｃＢＮ焼結体であって、前記焼結体には、平均粒径が１０ｎｍ以上２００ｎｍ以下のＷＳｉ２が、含有割合として１体積％以上２０体積％以下となるように分散されていることを特徴とするｃＢＮ焼結体。
  2. 　請求項１に記載のｃＢＮ焼結体で形成された工具基体を有することを特徴とする切削工具。
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CN111801304B (zh) 2022-08-12
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